<form id="frmLang" action="<?php echo url_for('@changeLang') ?>" method="post">
<select name="lang" onchange="submit('frmLang')">
  <option value="en" <?php if($sf_user->getCulture()=='en'){echo 'selected';} ?>>Inglés</option>
  <option value="es" <?php if($sf_user->getCulture()=='es'){echo 'selected';} ?>>Español</option>
</select>
</form>